The present invention relates to resistive strain gage pressure sensors and, in particular, to temperature compensation of such sensors.
Temperature changes in the operating environment of resistive pressure sensors produce significant errors in the pressure output signal of such sensors. Slight variations in the temperature coefficient of resistivity of a resistive bridge sensor causes an offset error and an apparent decrease in the flexibility of the diaphragm, thus causing a sensitivity error. Therefore, it is often necessary to compensate for temperature variations by measuring the temperature of the pressure sensor and correcting the pressure output signal.
Methods exist which partially correct temperature-induced errors in resistive pressure sensors. Many approaches use a separate temperature responsive element, for example a thermocouple, thermistor or diode. These elements measure a temperature near the pressure sensor and generate a correction signal dependent on the environmental conditions of the sensor. Other approaches involve selection of the thermal coefficients of the bridge circuit and temperature compensating elements, such as resistors, to integrally balance the bridge circuit.
A problem with such prior art approaches is that during dynamic conditions such as warmup, brief temperature excursions or other transient temperature conditions occur that often result in a phase lag between the pressure signal and temperature signal. Such a phase lag results from the non-perfect thermal coupling inherent between two separate electrical elements simultaneously receiving time-varying stimuli, such as temperature fluctuations which do not simultaneously reach and affect the temperature responsive element and the pressure sensor. Thus, error occurs in the correction of the pressure output signal.